Hearing Flashcards
what is the function of hearing
- Distinguishing different sounds
- Localization
Language
what does language do
- Production
- Comprehension
what are the 3 structures that allow hearing to take part
- Outer ear
- Middle ear
- Inner ear
what is the function of the central auditory nervous system
- Electrochemical action potentials
- Information processing
what is the outer ear divided into
Pinna
Ear Canal
what is the mode of operation of the outer ear
Air Vibration
what is the function of the outer ear
1) Protect ear
2) Localise
3) AMPLIFY
what is the middle ear divided into
Tympanic Membrane
Eustachian Tube
Small bones - stapes incus and malleus
what is the mode of operation of the middle ear
Mechanical Vibration
what is the function of the middle ear
1) IMPEDANCE MATCHING
2) Equalise pressure – Eustachian tube prevents a standing pressure difference on either side of the eardrum that would compromise function
3) Stimulate inner ear– the arrangement of ossicles transmits vibrational energy to the oval window, preventing it from being reflected away from the surface of the inner ear
what are the divisions of the inner ear
Cochlea
Semilunar canals
what is the mode of operation of the inner ear
Hydrodynamic (fluid)
Electrochemical
what is the function of the inner ear
1) Sound filtering
2) Signal Transduction
what is impedance matching
overcome the acoustic impedance between the air in outer ear and the fluid in the inner ear.
What are the two ways in which impedance matching is done
1) Transmission of Vibration through the Malleus, Incus and stapes, vibrations from transmitted ear to the bones causes a vibration ratio, so the malleus from the tympanic membrane moves 1mm the stapeus will move 1.3mm therefore there is a higher movement generated for fluid to move
2) Tympanic Membrane to Oval window area difference 22:1 this leads to Higher pressure generated over smaller area, these can overcome the high impedance of the cochlea and make the cochlear vibrate
what is between the middle ear to the outer ear
- it is all air
- but when you get to the cochlea (inner ear) there is fluid, the fluid is harder to get it to vibrate than the air therefore there is a higher resistance (impedance)
what part of the ear controls the transmission of sound
cochlear
what are the two parts of transmission of sound
- Frequency Transmission (High or Low Pitch) - Hz
- Amplitude Transmission ( Loud or Soft) - dB
describe how the cochlear transmits sound
- Cochlea is a tube turn 2 and ¾ turns
- Vibrations pass on as fluid movement via oval window
- Fluid movement converted to electrochemical information by cochlear cells
- Transmitted to brain via nerve
what are the 3 canals in the cochlea
- scala tympani (perilymph)
- cochlear duct (endolymph)
- scala vestibuli
how is the 3 canals separated
- The canal on the outside is the Scala tympani this is separated from the middle canal, the cochlear duct, by the basilar membrane, the cochlear duct is separated from the inner canal, Scala vestibuli, by the vestibular membrane
what are the inner and outer hair cells attached to
- Within the cochlear duct we have the Tectorial membrane from which the Outer air cells and Inner Hair Cells protrude.
- The inner cells are attached to the membrane and outer cells are suspended between supporting cells
describe the entire part of the cochlea
Entire organ: Organ of Corti
- Basilar membrane is floor
- Tectorial membrane is roof
- In between is the hair cells
what is within the cochlear duct
Tectorial membrane
what is in the organ of cortic
Outer and Inner Hair Cells
what are the outer hair cells involved in
- 3 Rows
– Suspended between supporting cells - Auditory Discrimination - they increase there sensitivities to specific frequencies of sounds
– amplify sound + discriminate sounds,
what are the inner hair cells involved in
- 1 Row
- Attached to the basilar membrane
- Frequency tuning
– split sound into different frequencies as they vibrate at different points along the membrane due to different frequencies
how do the inner and outer hair cells convert signals to electrical signals
Convert signals to electrical signals via K+ Channels
- converted to signals for the cochlear nerve
describe the structure of the basilar membrane
- Thin + Wide at Apex (low frequency)
- Thick + Narrow at Base (High frequency)
difference frequencies vibrate the basilar….
Different Frequencies vibrate the basilar membrane at different part
what does the amplitude of the sound wave mean
- it is the loudness
the louder the sound…
- the greater the amplitude
- the more the hair cells move
- the more frequent action potentials to the brain
what is the threshold of amplitudes
Threshold : 0dB Whisper: 40dB Normal Talking: 60-80 dB Discomfort : 100dB + Pain at : 140dB +
what is the threshold of frequency
Range: 20 Hz to 20 kHz
Most Sensitive: 1-4kHz
describe the auditory pathway
- it goes from local nuclei in the medulla
- to the pons
- to the midbrain
- to the cerebellum
what is the cochlear nerve part of
- Cochlear part of Vestibulocochlear nerve
- CN 8
where is the cochlear nucleus
- it is in the medulla there are two types (ventral and dorsal)
what are the two types of cochlear nucleus
- Ventral : Loudness (intensity) and Timing (for location)
- Dorsal : Pitch and quality
describe how the auditory pathway works,
1) Cochlear Nucleus in Medulla : 2 kinds
- Ventral : Loudness (intensity) and Timing (for location)
- Dorsal : Pitch and quality
2) Superior Olivary Nucleus (Pons)
Spatial localisation
3) Inferior Colliculus (midbrain)
4) Medial Geniculate Nucleus (midbrain)
5) Primary auditory cortex in temporal lobe
- Processing sound
what does the ventral cochlear nucleus project into and what is it control of
- Project into superior olivary nucleus
- Stellate cells: Intensity
- Bushy cells : Timing
where does the dorsal cochlear nucleus project into and what is it in control of
- Project to lat. Lemniscus going to inferior colliculus
- Pitch, quality
what does the superior olivary nucleus do
Uses to localise sound location via
1) Inter – Aural TIME difference
2) Inter Aural LEVEL difference
what is intra aural time difference
- It time difference between sound reaching one ear from another
- FOR LOW FREQUENCY SOUNDS (as take longer time to reach)
what is intra aural level difference
- it is Difference in sound pressure between two ears
- FOR HIGH FREQUENCY SOUNDS
what is for high frequency sounds
intra aural level difference
what boradmann area is the primary auditory cortex
41
what is the function of the primary auditory cortex
- Identify complex sound
- Detect changes
- Behaviourally relevant sound
- Attention with sound
- Language and music
how do you detect damage to damage to auditory apparatus
TUNING FORK TEST:
- Weber’s
- Rinne’s
what is testing damage to auditory apparatus for
- sensorineural or air conduction deficit
what is the tuning used for detecting damage to the auditory apparatus
512 Hz
what happens when there is an issue with air conduction
- the Bone Conduction Usually not as good as air conduction
- if the bone conduction is better it is because there is problem in air conduction along the ear canal route through tympanic membrane
what are the causes if there is an issue with air conduction
Fluid in the ear
Ear Wax
what happens when there is an issue with sensorineural damage
- issue lies in the inner ear and nerve, for example neurone conduction
what are the causes to sensorineural damage
Inflammation: Ear infection affecting cochlea/nerve
Trauma
Tumor : Neuroma
Ototoxic Drugs
How does Webers test work
- Place tuning fork in middle of forehead
- Ask where is it louder?
- Tells you which ear is affected
Normal: Same on Both sides
Positive - Abnormal: Louder on one side - Air Conduction defect on this side OR - Sensorineural defect on other side
Why does Webers test work
Using a Weber Test, we are using Bone Conduction and Air Conduction to test for sound at the same time (vibrations travel through the bone and the air in the middle ear)
- If It is equal, bone conduction and air conduction is occuring normally on both sides and equally as it is synchronised.
- If there is a air conduction is affected on one side, the bone conduction and air conduction are not synchronised. This interaction makes the sound louder on that side
- A sensorineural defect on the opposite side however will means that any sound is not being transmitted well on that side by neurones so the normal side will automatically be louder
How does Rhines test work
- Vibrating tuning fork first placed on the Mastoid
- Then when it stops buzzing,
- Place next to ear
Ask them which felt louder
Normal : Sound is heard louder next to the ear
Positive- Abnormal:
Sound louder on the mastoid – air conduction defect on the same side
what happens during the Rhines test
Comparing again Bone conduction ( on mastoid ) to air Conduction ( putting tuning fork next to ear)
Normal: Air conduction is normally better than bone conduction. Hence, in a normal test, the sound should be heard better with air conduction when tuning fork is next to the ear.
Abnormal:
If Bone conduction is louder i.e. Tuning fork on mastoid is louder , therefore There is air conduction issue on this ear.
why does the Rhine test not work on sensorineural deafness
Sensorinerual deafness however, the Rinne Test is normal, Because the problem is not in air conduction itself but the transmission via neurones.
what are the two types of deafness
- air conduction
- sensorineural deafness
How do you conduct the tests, in which order and why
Do a Webers test first:
- Determine which side is louder
- Either Air Conduction defect this side or sensorineural on other side
Do a Rinnes Test on the Louder side:
- If Bone conduction is better, there is air conduction defect on this side.
- If not, the defect is probably sensory neural on other side
what are the two functions of auditory reflexes
- Prevent damage to the person and the ear
2. To distinguish important sounds from background
How does the attenuation reflex happen
- This relies on activation of the middle ear muscles
- Activated by own voice or loud sounds
- Dampens out low frequency sound – this allows better discernment of speech
how does the startle reflex work
- Ducking down to protect the back of the neck (whole body startle) and closing the eyes (blink)
what are stern cilia
- these are projections from the hair cells that are embedded and connected to the tectorial membrane
what do outer hair cells look like
- they have a horse shoe shape
sterocillia are a form of…
mechnoreceptors
how do you work out the loudness of sounds
- dB = 20log P/Pr
- P= pressure of incoming sound
- Pr= pressure of reference (20uN/m2)
- = pressure of just audible sound
what are middle ear disorders
- Glue ear – build up of mucus within the middle ear, prevents normal motion of the ossicles and prevents sound pressure equalization
- Performation of the tympani membrane
what happens if the angular gyrus is damaged
- Alexia - can’t read
- agrpahia - can’t write
- but you can comprehend speech and speak
